Variable condenser



C. P. BROCKWAY VARIABLE QONDENSER July 5 9 I Filed Nov. 22, 1923 2 Sheets-Sheet l In I.

- I N V EN TOR. Carl R Broc/rn'ay ATTORNEY July 5 1927.

c. P. BROCKWAY .VARIABLE CONDENSER Filed NOV. 22, 1925 2 Sheets-Sheet 2 v HEI E Q, .7 I00 E EMXIL hcHX- 7' INVENTOR.

tar! 1? Bro ckway 52 lckX- ag l M v ATTORNEY.

Patented July 5, 1927.

UNITED STATES 1,634,930 PATENT OFFICE.

CARL P. BROCKWAY, OF TOLEDO, OHIO, ASSIGNOR TO THE ARCTURUS RADIO ('10., OF HARRISON, NEW JERSEY, A CORPORATION OF DELAWARE.

VARIABLE CONDENSER.

Application filed November 22, 1923. Serial No. 676,224.

Another important object is to increase the total capacity variation of the condenser so that the range of adjustment is widened.

An important, object of the invention is to provide a condenser in which at low capacity values sensitive adjustment of the condenser is made possible without employment of Vernier or similar accessories.

A further object of the invention is to provide a variable condenser in which the capacity increment at closer position of the plates is greater than that of a straight line.

Another important object is to flatten out.

the capacity curve in the range including the maximum capacity values.

Another object comprehended is the employment of capacity varying means whereby the capacity curve of the condenser for change of capacity with varying relative position'of condenser plates may be made at will.

Other objects, and objects relating to de tails of construction and economies of manufacture, will appear as ,I proceed with the description of that embodiment of the invention which may be preferred and which, for the purposes of the present application, I have illustrated in the accompanying drawings, in which:

Figure I is a plan view of a condenser embodying the invention.

Figure II is asection taken substantially on line 11-11, Figure I, showing the parts on a magnified scale.

Figures III and IV are detail plan views of the lower and upper plates respectively.

Figures V, VI. VII and VIII are' diagrammatic views illustrating the relative degrees of curvature of the two plates at various positions of the adjusting knob and disc, beginning with a position in which the latter is unscrewed 720 degrees from its furthest in position.

Figures IX, X and XI are diagrammatic sections similar to Figures V, VI,-VII and VIII illustrating the variation of curvature of a modified form of the condenser, the sections being through the lower plate adjacent the central aperture.

Figure XII is a view showing four curves indicating the capacities obtained during given rotations of, first, the ordinary multiple plate condenser. second, the condenser of my previous application, third, the condenser of the present application, and fourth, the modified condenser of the present application.

Similar reference numerals indicate like parts throughout the several views.

In the drawings, indicates a block of suitable insulating material having a circular rim 11 enclosing a circular recess adapted to receive a lower, resilient, bowed condenser plate 12, a dielectric sheet 13, preferably of mica, and an upper, resilient condenser plate 14 bowed in the same direction as the plate 12, but with a sharper degree of curvature.

The block 10 is adapted to be mounted upon an instrument board 8 or other suitable support. This is accomplished primarily by a bolt 16 having an elongated cylindrical head 17 the base of which bears against the edges of a hole bored through the center preferably of the block 10. Another hole is bored through the instrument board 8 of sufficient width to include both the bolt and the holding nut 18 screw-threaded thereto and adapted to bind the bolt to the block base 10.

Screw-threaded also on the bolt 16 is a second nut 20.below the nut 18, the nut having the function of holding the instrument on the instrument board 8. To this end, a washer 19 intermediate the two nuts is adapted to contact with the instrumentboard 8 and be held thereupon by the nut 20. The nut 20 serves also, where expedient, as a connector for a ground to the bolt 16, in order to reduce the efl'ect upon the condenser of-the hand of the operator on the knob.

The two binding posts may also be so constructed as to assist in fixing t e condenser upon the instrument board. T ese binding posts are mounted preferably in countersunk holes in the block 10. As shown in Fig. II,

the beveled head of the post 21 is caused to draw the metal of the lower plate 12 closely down upon the walls of the countersink,

forming a good electrical contact, as well as a secure and rigid mounting of the plate upon the block 10. A threaded bushing 22 is set into or against the lower side of the instrument board and constitutes a securing nut for the binding post, while upon the end of the latter is threaded a binding nut 23 of conventional design. Direct connection between the lower plate 12 and the binding post 21 is had only through a narrow finger 2 1 formed ,by cutting slots into the plate 12 from one edge (see Fig. III). thus leaving the edge of the plate otherwise tree to slide and rock as its adjustment is changed.

The binding post 25 for the upper condenser plate 14, engages a similar narrow finger 26 integral with the plate and cut back into the same, as clearly shown in Fig. IV, this finger having the same purpose as the finger 24. The post 25 in addition, anchors the dielectric plate 13. It passes through a threaded bushing 27 and is provided with a binding nut 28 similar in all respects to the bushing 22 and nut 23 on the post 21.

The head 17 on the central bolt 16 is threaded as shown in Fig. IT to receive an internally threaded bushing 29 mounted centrally in the knob 30 and'adjusting disc 31, by means of which the disc is caused to move towards or away from the block 10. The disc 31 fits rather closely Within the receptacle formed by the block 10 and rim 11, and thus constitutes a cover for the receptacle to protect the parts therein mounted. 32 is a wear plate preferably made of fibre and set into a shallow recess in the bottom of the disc 31.

Each of the plates 12 and 1 1 has a central hole large enough to clear easily, the cylindrical head 17 in all positions of adjustment of the plates. The latter being bowed in the same direction with ditierent degrees of curvature, and each being attached to the base in a manner to permit of their sliding readily with respect to each other, it will be obvious that as the knob 30 is screwed down upon the threaded head 17, the upper plate will first approach the lower one at the center, its free edge sliding upon the block 10. The curvature of the upper plate is thus caused to gradually approximate that of the lower one. As soon as pressure is transmitted through the upper plate and intervening dielectric to the center of the lower plate, both plates. begin to move and continue to do so throughout the remainder of the range of adjustment, the area of close proximity of the two plates being gradually increased. The principal effect of the last portion of the dial movement is to straighten out the lates and the last crowding together of the p ates is therefore spread over a much greater are of dial movement than has been possible heretofore.

The series of diagrammatic views of Figs.

V to VIII inclusive shows in a very rough Way, what I believe takes place with respect to the curvature of the plates as the the center portion of the upper plates has 7 approached to the under plate, the two plates being approximately equidistantly separated. In Figure VII. the plates are closest at their central portions. and in Figure Vlll. the plates are in close contact. Figures IX. X and XI show variations in the plates in a modified form of condenser. In this modification, there is formed a central depression in the lower plate (see dotted line of Fig. III) which at its base contacts with the condenser base 10. The depression 50 joins the outer part 51 of the plate in a smooth reversed curve. In this form 03": condenser as the pressure is applied to the upper plate, it moves toward the lower plate, contacting first at the point 52, as shown in Fig. X, and subsequently contacting throughout its area, as indicated at Figure XI. The function of the depression 50 in the lower plate is to flatten out the capacity curve in the critical range as well as to increase the total range of capacity change as will be hereinafter more fully described.

The curves of Fig. X11 indicate the capacities at various degrees of rotation of the adjusting knob of four different condensers. The light dot and dash line 1 shows the capacity of the usual multiple plate condenser, in which one series of spaced plates swings into the spaces between the plates oi another set, the plates of the latter set being fixed. In this type of condenser, a 180 degree movement is all that is possible. The dotted line 2 shows the capacity of the condenser disclosed in my prior application, Serial Number 558.976, for the various positions of the adjusting knob throughout 720 degrees of movement. In this form. the lower plate is fiat and fixed. The heavy dot and dash curve 3 shows the capacity of the first condenser of my present application at the various positions of adjustment.

The full line curve 4 shows the variation in capacity for difierentadjustments of the modified condenser of the present application.

Tn examining these curves. emphasis should be made of various important interpretations thereof. The chief distinction between the conventional condenser curve 1 and the remaining curves lies in the fact that the total capacity variation of curve 1 occurs in the short range of 180, a small rotation of the movable condenser plates resulting in a relatively pronounced change in capacity.

This sensitiveness of change involves difliculties in accurate adjustment, particularly in the more sensitive range of the condenser between the minimum and 0.0004 micro farad.

In applicants condensers, however, the maximum capacity change is distributed over a range of 720 degrees, the slope of the curve in the active used portions being no tably less than the slope of curve 1. This characteristic is valuable in permitting a small change of capacity for a considerable range of rotation of the dial, thus allowing very accurate ad'ustment, especially in the sensitive range 0 the condenser.

Another advantage of applicants con denser as disclosed in the curves lies in the fact that in the capacity range between 0.0004 and 0.0006 micro farads where the effect of capacity variation is less marked for a given change in capacity, the curves 2, 3 I

and 4 are much steeper than in the ranges preceding. This characteristic indicates that after the condenser has received a certain charge and is therefore less sensitive to fixed increments of charge, a larger amount of capacity is available to augment the total capacity effect in the circuit, or, as may otherwise be stated, in the steeper ranges of the curves, the percentage increase of total condenser capacity per degree change of dial position tends. to approach a constant value.

Distinguishing between the curves 2, 3 and 4, it is evident that the total capacity change is greater. in the condensers having the flexible lower plate 12 as incorporated in the present invention, than in the condenser having a fixed lower plate as incorporated in applicants co-pending application, heretofore referred to. It is further apparent that the condenser corresponding to curve 4 not only has a larger capacity value for the range between 0.0002 and 0.0006 micro farads, but also the total ca acity change from 0 to 720 is greater, t e minimum at 0 being less than that for the condenser without the central depression or the ordinary rotatable condenser of curve 1. This last factor is important in that for a given maximum capacity of the condenser, a greater change of capacity is available for use in capacity adjustment of circuits. Another factor lies in the fact that in the range exceeding 0.0004 micro farads, the slope of curve sion in the lower plate or a variation of ourvature in either plate to magnify or modify the characteristic curves depending on the requirements of the circuit. Y

Having thus described my invention, what I desire to secure by United States Letters Patent and claim is: s

1. In a condenser, a pair of resilient bowed plates, said plates being bowed in the same direction but in different degrees; means to cause said plates to approach a relative uniformity of curvature and to thereaftermove closer together whereby the capacity of said plates is gradually varied.

2. In apparatus of the class described; a pair of condenser plates separated by a solid dielectric, said plates being resilient and bowed in the same direction, but in different degrees; and means for causing said plates to move towards each other gradually and to assume substantially the same curvature before the limit of their movement. toward each. other is reached.

3. In apparatus of the class described; a pair of condenser plates separated by a solid dielectric, said plates being resilient and bowed in the same direction, the curvature of the upper plate being greater than-v that of the lower plates; means for supporting both plates at the edges thereof and means for applying pressure to the upper plate near the center.

4. In apparatus of the class described; a

ase; a pair of resilient, bowed condenser plates separated bya solid dielectric, the lower plate being formed with a relatively narrow finger cut back into one edge; means for attaching said finger to the base, the upper plate being also formed with a relatively narrow finger out back into the opposite edge; means for attaching. said finger to the base beyond the adjacent edge of they Y lower plate. said plates being bowed in the shape of said displaced portions and for.

moving the displaced portions of the conducting plates toward each other.

6. In a condenser; the combination of a non-conducting base; a pair of superimposed curved conducting plates secured at one edge to said base, the attached edge of one plate being opposite ,to the attached edge of the other plate and the upper of said plates having a free contact on said base beyond the point of attachment of the edge of the lower plate. said plates being curved in the same direction, and said upper plate having a shorter radius of curvature than said lower plate; a flexible dielectric interposed between the plates; and means for flexing said plates.

7. In a condenser; the combination of a non-conducting base; a flexible conducting plate secured to said base and concavely curved relative thereto; a second flexible conducting plate secured to the base intermediate the first plate and the base, said second plate being curved concavely toward its periphery and convexly toward its interior relative to the base, said first plate having a greater curvature than said second plate; a flexible dielectric interposed between said plates; and means for flexing the plates.

8. In a condenser; a base; a curved conductor plate secured to the base at one side and freely contacting with the base at the other side; a second curved conductor plate in jux taposition with the first plate curved in the same direction but having a smaller radius of curvature than said first plate and secured to said base adjacent the free end of said first plate, the free end of the second plate having free contact with the base; a dielectric plate between the conductor plates; and gieans for moving the plates toward the ase. In testimony whereof, I allix my signature.

CARL P. BROCKXVAY, 

